1. Field of the Invention
The present invention relates to a connected sensor system for monitoring a state of an object to be detected, and also relates to a network unit and a sensor unit used for the connected sensor system.
2. Description of the Background Art
In an automated manufacturing line, many sensors for detecting workpieces are arranged in proximity to the workpieces so as to reliably detect the position, the presence/non-presence, the state, and the like of the workpieces.
In this kind of sensor system, it is cumbersome to prepare wirings between many sensors and a control apparatus of the sensors. Therefore, a connected sensor system is utilized, in which these apparatuses are made into units and each unit is connected by physically coupling each unit, so that wirings between the units are completed at a time. In the connected sensor system, many sensor units are connected in proximity to a workpiece, and many sensor heads such as optical fibers connected to each sensor unit are arranged in proximity to a portion of a workpiece to be monitored. In the connected sensor system, a detection signal output from each sensor unit is collected and monitored by a host control apparatus.
Normally, a sensor unit has an external input function to receive and execute various setting signals provided from the outside. Each sensor unit determines the received external input signal. When the external input signal is determined to be a signal pattern of external input, a previously-defined external input function is executed. The external input to each sensor unit is executed by an operation switch arranged on each sensor unit. Alternatively, when the sensor unit has an external input terminal, an external input line connected to this external input terminal is connected to an output terminal of a host control apparatus such as a PLC, and the host control apparatus gives an external input to each sensor unit. A previously-defined external input function is executed, triggered by this external input (for example, Japanese Patent Laid-Open No. 2006-003136).
However, when the user uses the operation switch to perform external input operation, the operation is extremely cumbersome especially in a sensor system including a plurality of connected sensor units. In addition, there is a problem in that an external input cannot be given to all the sensor units at a time or an external input cannot be given at a desired timing. In a case where the external input signal is input via the external input line from the host control apparatus, it is necessary to individually connect each sensor unit and the output terminal of the host control apparatus via a cable, and there is a problem in that the wiring is cumbersome and the connected wires become more complicated.
In contrast, the following configuration has been known. A plurality of sensor units are connected to one network unit, and this network unit is connected to a host control apparatus via a field bus so as to relay communications of the plurality of sensor units. In this configuration, a communication command for accessing an address in the network unit for communicating with each sensor unit may be set by the host control apparatus side, so that the host control apparatus can individually give an external input to each sensor unit via the network unit. According to this configuration, an external input can be given to each sensor unit, without manipulating the operation switch of each sensor unit and without making the wiring complicated.
However, when the host control apparatus gives an external input to each sensor unit via the network unit, it is necessary to design a communication command for each sensor unit. Accordingly, the user needs to understand the specification of the communication command and design a communication command with a ladder program and the like. Therefore, there is a problem in that it is not easy for the user to use it.
The present invention is made in view of the above problems, and it is an object of the present invention to provide a connected sensor system which can be easily used by the user and which can give an external input to each sensor unit without making the wiring complicated, and to provide a network unit and a sensor unit used for the connected sensor system.